## Search found 54 matches

Tue Oct 22, 2013 12:43 am UTC
Topic: 1280: "Mystery News"
Replies: 42
Views: 10936

### Re: 1280: "Mystery News"

As someone who uses a mobile 4G dongle for Internet at work, with a very limited download quota and high excess surcharges, I really wish news sites would get out of the habit of auto-playing videos that have basically the same information as what's in the text of the article. What's worse is when t...
Mon Sep 03, 2012 12:35 am UTC
Forum: Coding
Topic: Bug in GLPK?
Replies: 1
Views: 1239

### Re: Bug in GLPK?

I discovered where the problem is. The bounds of the decision variables in the MPS file go from 0 to 1.

Obviously this is not analogous to the model in the Lingo file. Hence, Lingo MPS export is screwed.
Fri Aug 31, 2012 1:44 am UTC
Forum: Coding
Topic: Bug in GLPK?
Replies: 1
Views: 1239

### Bug in GLPK?

I'm very new to GLPK but have been using Lindo Systems' Lingo for quite some time. I'm trying to compare the performance of Lingo vs GLPK. (For those interested, Lingo beats GLPK in most cases by a time factor of 2, but in some rare cases GLPK beats Lingo by a time factor of 2. Interesting results!)...
Wed Oct 26, 2011 6:33 am UTC
Forum: Mathematics
Topic: Help me with higher radix Cooley-Tukey FFT
Replies: 2
Views: 1682

### Help me with higher radix Cooley-Tukey FFT

I'm trying to implement a radix-3 Cooley-Tukey FFT in C, and when I get that down I will move on to higher radices. I've already written the radix-2 case. For the radix-2 case: The mathematics is simple. We start off with the naive sum for the DFT and split it into 2 interleaved halves. We can take ...
Wed Nov 24, 2010 11:59 pm UTC
Forum: Mathematics
Topic: Calculus 2 question.
Replies: 3
Views: 656

### Re: Calculus 2 question.

I did a little Newton walk, and found that Sin[x] == x 2 when x==0 and x~=0.8767262153950625 That number looks unfamiliar to me, so I can't think of a closed-form off the top of my head. It's possible that there is no closed form at all, as others have said. 0.876726215395062445972118643141928139971...
Thu Nov 18, 2010 10:27 pm UTC
Forum: Coding
Topic: C# TCP/IP Game problems
Replies: 11
Views: 6427

### Re: C# TCP/IP Game problems

Yeah, I'm using stream.write() and then stream.flush() which I assume makes it send a partially-full packet out. So I've come up with the following scheme which will use bytes instead of strings: Server->Client {L}{'S'}{SPad1}{SPad2}{Bx1}{Bx2}{Bx_}{By1}{By2}{By_}{S}{Chk} = 12 bytes Client->Server {L...
Thu Nov 18, 2010 9:08 pm UTC
Forum: Coding
Topic: C# TCP/IP Game problems
Replies: 11
Views: 6427

### Re: C# TCP/IP Game problems

As soon as I start trying to send them more quickly, then they start getting jumbled together. When I say jumbled together, I mean 1 buffer and the next buffer come through together, with double the length. That's just how it is. TCP acts like a stream, and you receive any data that is available to...
Thu Nov 18, 2010 11:33 am UTC
Forum: Coding
Topic: C# TCP/IP Game problems
Replies: 11
Views: 6427

### Re: C# TCP/IP Game problems

I'm using: ASCIIEncodingencoder = new ASCIIEncoding(); bytes[] buffer = encoder.GetBytes("This is a message to send."); networkStream.Write(buffer, 0, buffer.Length); and then to receive, I have a thread which goes something like: byte[] message = new byte[1024]; int bytesRead; while (true...
Thu Nov 18, 2010 7:36 am UTC
Forum: Coding
Topic: C# TCP/IP Game problems
Replies: 11
Views: 6427

### C# TCP/IP Game problems

I'm writing a multiplayer 'Pong'-style game using C# (.Net 3.5 SP1 to be exact). The game runs absolutely flawlessly over a loopback connection, and also over my home LAN connection, however over the Internet very strange things start to happen. So this is what happens: (and try not to laugh, this i...
Tue May 25, 2010 1:39 am UTC
Forum: Mathematics
Topic: Convolving two images
Replies: 3
Views: 816

### Convolving two images

This thread could go in either math/programming, but I think it fits here a little better. Last night I wrote a small program that takes two equally-sized images with dimensions being a power of two, and performs a 2D FFT on them. (Actually, 3 2D FFTS, one for each colour channel). Then, the resulti...
Wed May 05, 2010 12:03 pm UTC
Forum: Coding
Topic: C#, launching form from console app
Replies: 1
Views: 828

### C#, launching form from console app

I have a C# console app which runs a small simulation. A bunch of stuff flashes on the console and it's all fancy schmancy, but it's not very useful in terms of visual information. I've created a class called Visualization. This class has a method called update( ... ) which gets the data from the pa...
Wed May 05, 2010 12:52 am UTC
Forum: Mathematics
Topic: Network balancing algorithm
Replies: 11
Views: 2788

### Re: Network balancing algorithm

Ok, so I was thinking about this while trying to sleep, and I think I have a fairly workable algorithm. t0 represents the initial state of the network, however random. We work out, for each node, the difference vector between its current position and the weighted average of all the connected nodes. ...
Tue May 04, 2010 4:27 pm UTC
Forum: Mathematics
Topic: Network balancing algorithm
Replies: 11
Views: 2788

### Re: Network balancing algorithm

@OP: I'd probably start by randomly placing the nodes, then randomly picking a node and moving it a little so that the total length of the edges connecting it to the other nodes are least, and the distances to the nodes it isn't connected to are increased. Yes, this is what I have started experimen...
Tue May 04, 2010 10:53 am UTC
Forum: Mathematics
Topic: Network balancing algorithm
Replies: 11
Views: 2788

### Re: Network balancing algorithm

Syrin wrote:Make a circle.

I guess it serves me right for not being more specific...

let's say my objective is to minimise the length of each link, while still maintaining a minimum distance between each node.
Tue May 04, 2010 6:51 am UTC
Forum: Mathematics
Topic: Network balancing algorithm
Replies: 11
Views: 2788

### Network balancing algorithm

Hi let's say I have n+1 nodes which are connected to between 1 to n other nodes. I wish to arrange this network visually as a picture, and hence need some sort of algorithm to determine where to put the nodes. What is this problem called, so that I can find some information on some solutions? Thanks...
Mon Jan 11, 2010 10:24 am UTC
Topic: 0687: "Dimensional Analysis"
Replies: 159
Views: 62477

### Re: "Dimensional Analysis" discussion

Note sure why this isn't working, but could probably work this out on paper if I wasn't too lazy: http://www.wolframalpha.com/input/?i=Solve[(0.5433+MWh+/+345+GPa)+*+(((48%2Ba*51)/2)+Mpg+/+34+Km)%3D%3DPi,+a] Instead of working out a simple average between highway and city mileage for the Prius, you ...
Sat Nov 14, 2009 12:20 pm UTC
Forum: Mathematics
Topic: Laplace Transforms
Replies: 2
Views: 517

### Re: Laplace Transforms

Seems like an indirect way to ask for the inverse transforms of these functions... using these ? Sorry I should have mentioned this... he specifically asked not to compute the inverse transforms. Just to show that they are Laplace transforms. I'm not at all an expert in this, but it seems like a bi...
Sat Nov 14, 2009 6:30 am UTC
Forum: Mathematics
Topic: Laplace Transforms
Replies: 2
Views: 517

### Laplace Transforms

I know some of you are a little touchy about this, so I'm going to start by saying this is not homework - I'm working through a past exam paper in preparation for an exam I have in a couple of days. The question says: Explain why the functions F(s) = \frac{s^2+4s+17}{s^5+16s^3+2s^2+6} G(...
Mon Nov 09, 2009 2:04 am UTC
Forum: Science
Topic: Physics/Optics: bands, modes, etc
Replies: 3
Views: 492

### Re: Physics/Optics: bands, modes, etc

2a & b) An arbitrary structure has its distinct boundary conditions that restrict the characteristics of the wave that can travel in the structure. For example, if the wave function must equal zero at the edges of the structure, then the wave would be a sine (rather than cosine) if you define o...
Sun Nov 08, 2009 2:29 am UTC
Forum: Science
Topic: Physics/Optics: bands, modes, etc
Replies: 3
Views: 492

### Physics/Optics: bands, modes, etc

Hi science people. Firstly, I'm a maths graduate trying to write a thesis on a maths/physics topic, and I'm having a little trouble getting my head around some of the physics concepts which I really should know. I'm sure I can find the answers to some/most of these in a book somewhere, but my deadli...
Mon Oct 19, 2009 11:04 am UTC
Topic: 0651: "Bag Check"
Replies: 206
Views: 52247

### Re: "Bag Check" Discussion

I remember a little over a year ago I was arguing with a lady at the airlines over the phone. They didn't sell my contact lens solution in smaller bottles, and you're not supposed to change brands of contact lens, or contact lens solution without first contacting your optometrist and going through a...
Thu Oct 01, 2009 10:26 am UTC
Forum: Mathematics
Topic: Differentiate the Bessel function
Replies: 2
Views: 1176

### Re: Differentiate the Bessel function

No that's ok... I figured it out by differentiating the flux integral definition. Thanks anyway.
Wed Sep 30, 2009 12:09 pm UTC
Forum: Mathematics
Topic: Differentiate the Bessel function
Replies: 2
Views: 1176

### Differentiate the Bessel function

What are the steps involved in differentiating the Bessel function [imath]J_\alpha(z)[/imath] ??
I already know the answer: [imath]J_\alpha'(z) = \frac{1}{2}[J_{\alpha-1}(z) - J_{\alpha+1}(z)][/imath], but I'm at a loss as to how to do it on paper?
Sat Sep 19, 2009 10:23 am UTC
Forum: Mathematics
Topic: Discrete Fourier transform - frequencies
Replies: 0
Views: 488

### Discrete Fourier transform - frequencies

Hi, So if I have an equally spaced list of values in the time domain, and I do a discrete fourier transform, I can recover the frequencies of that list by freq = k*\frac{1}{n}dt where freq is the frequency, k is the k from x_{k} , dt is the (constant) difference between each consecutive sample, and ...
Sat Sep 19, 2009 7:02 am UTC
Forum: Coding
Topic: Using FFTW in C++
Replies: 6
Views: 7156

### Using FFTW in C++

Hi all, I've been trying to get this 2D fourier transform working for so long now, and I'm asking here as my final desperation. I'm using C++ on a unix machine. I have a bunch of 2d complex data which needs to be fourier transformed. The data is very periodic in the X direction, and not very periodi...
Sat Sep 12, 2009 11:20 am UTC
Forum: The Help Desk
Topic: GNUPlot anyone?
Replies: 1
Views: 732

### GNUPlot anyone?

I have 15 columns... x, y, z, and 12 columns of data. y is constant at 0, and I'm wanting to plot 1 of the columns of data against x and z. I'm typing the following: splot "data" using 1:3:4 and I get a surface plot with a jillion red crosses - as expected. When I type: set pm3d splot &quo...
Wed Sep 09, 2009 2:39 pm UTC
Forum: Mathematics
Replies: 3
Views: 891

Thanks for that.. I'll keep that in mind for next time.

I actually got fed up with it and wrote my own 1D and 2D discrete Fourier transform in C++ to do what I needed... it's about a bajillion times faster than Mathematica.
Sun Sep 06, 2009 4:12 am UTC
Forum: Mathematics
Replies: 3
Views: 891

Hi I wasn't sure whether to put this into programming or mathematics. It is technically a programming question, though I'm not sure how many of the Programming regulars use Mathematica - which is basically just for mathematics anyway. Please don't yell at me if you disagree with my logic. I've got c...
Mon Jul 13, 2009 11:40 pm UTC
Forum: Coding
Topic: Mouse control in VBS?
Replies: 10
Views: 2689

### Re: Mouse control in VBS?

Nothing suspicious about it... I want to write a bot for Happy Farm on Facebook - that will automatically try to plant and harvest stuff every hour or so. Terms and conditions usually prohibit that sort of thing. You'll certainly get banned from Happy Farm if they discover it. I didn't think to che...
Mon Jul 13, 2009 7:39 am UTC
Forum: Coding
Topic: Mouse control in VBS?
Replies: 10
Views: 2689

### Re: Mouse control in VBS?

RoadieRich wrote:It sound suspiciously like he wants to build a bot for some sort of online game...

Nothing suspicious about it... I want to write a bot for Happy Farm on Facebook - that will automatically try to plant and harvest stuff every hour or so.
Mon Jul 06, 2009 11:51 pm UTC
Forum: Coding
Topic: Mouse control in VBS?
Replies: 10
Views: 2689

### Re: Mouse control in VBS?

...I guess not?
Sun Jul 05, 2009 8:39 am UTC
Forum: Coding
Topic: Mouse control in VBS?
Replies: 10
Views: 2689

### Mouse control in VBS?

I'm trying to find documentation on how to control the mouse from a VBS file. I just want to automate something on a website that will move the mouse to a bunch of different points and 'click'. I have previously automated somewhat complicated things like software installations by simulating keystrok...
Sat Jul 04, 2009 6:44 am UTC
Forum: Science
Topic: Liquid water
Replies: 6
Views: 1173

### Liquid water

Please, tell me WHY is it necessary for liquid water to exist in order for life to exist? As long as you have some source of energy - a sun, radioactive decay, heat, etc... and the raw materials present for reproduction, isn't that enough for life? We are basically nothing more than incredibly compl...
Mon Sep 08, 2008 2:25 pm UTC
Topic: 0473: "Still Raw"
Replies: 238
Views: 39698

### Re: "Still Raw" Discussion

I don't understand why the plane on the conveyor belt has stirred up so much discussion on the internet. Everybody knows that it's the wind moving over the curved wings that generates lift. It's irrelevant that that engines are going and the wheels are spinning... if there isn't a sh*tload of wind g...
Mon Aug 25, 2008 2:53 pm UTC
Forum: Science
Topic: Gamma Ray Bursts
Replies: 2
Views: 1075

### Gamma Ray Bursts

Apart from the fact that a GRB within something like 50,000 lightyears heading in our directions would instantaneously end all life on earth... I was curious about one thing: What would happen to our sun? Would a GRB have any affect on our sun at all, if there was one heading straight for it? What a...
Fri Aug 08, 2008 5:57 am UTC
Forum: Science
Topic: Black Hole Sun
Replies: 36
Views: 4371

### Re: Black Hole Sun

Well that makes more sense. I guess I misunderstood what I had heard.

It is difficult to visualise all directions pointing towards the centre.
Fri Aug 08, 2008 5:16 am UTC
Forum: Science
Topic: Black Hole Sun
Replies: 36
Views: 4371

### Black Hole Sun

Won't you come. Black holes are generally referred to as a point of infinite mass and infinite gravity. The star that collapses into a black hole has finite mass, so how can the black hole have infinite mass? Also, I'm not understanding the event horizon - apparently it is the point at which you can...
Wed Jun 18, 2008 5:41 am UTC
Forum: Mathematics
Topic: Interpolation using Mathematica
Replies: 2
Views: 1412

### Interpolation using Mathematica

I'm somewhat familiar with Mathematica, but not with all the nitty gritty stuff. I wrote a program in C++ that generates mandelbrots, and I pass in parameters such as max iterations, and resolution. These are both just constant integers. I want to build a function that will predict how long it will ...
Tue Jun 17, 2008 4:34 pm UTC
Topic: 0437: "SUV"
Replies: 181
Views: 28587

### Re: "SUV" Discussion

We're paying \$1.60/litre in Australia.
Fri Jun 06, 2008 2:33 am UTC
Forum: The Help Desk
Topic: LiveCD for virtualisation
Replies: 3
Views: 1207

### LiveCD for virtualisation

I'm not sure if this is the right forum to ask in. I would like to build my own linux LiveCD to virtualise several XP or Vista operating systems. I suppose the host system will be 64-bit, with maybe 4 or 8Gb ram, to give each of the 4 guest systems about 1 or 2Gb each. The host system will have a ha...